The aqueous humor of the human eye is known to contain hydrogen peroxide at concentrations higher than those in most other tissues. Hydrogen peroxide is relatively non-toxic in micromolar conentrations, but may serve as a stable precursor for more potent toxic oxidant species. Present investigations center on the role of hydrogen peroxide as a toxic oxidant precursor, mechanisms of hydrogen peroxide activation, identification of hydrogen peroxide-derived oxidants, and the role of hydrogen peroxide activation in diseases of the lens and other ocular tissues.